Heat and Mass Transfer
Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)

RN = hl/k
RN = ρ V l /μ
RN = μ cp/k
RN = V²/t.cp

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Heat and Mass Transfer
The time constant of a thermocouple is

Determined by the time taken to reach 100°C from 0°C
The time taken to attain 50% of the value of initial temperature difference
The time taken to attain 63.2% of the value of initial temperature difference
The time taken to attain the final temperature to be measured

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Heat and Mass Transfer
According of Kirchhoff's law

Emissive power and absorptivity are constant for all bodies
Radiant heat is proportional to fourth power of absolute temperature
Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body
Emissive power depends on temperature

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